1. Field of the Invention
This invention concerns a mandibular distraction apparatus and its manner of use, and more particularly relates to an intraoral mandibular distraction apparatus for temporary attachment to the teeth and bone to produce osteogenesis by patient manipulation preparatory to an orthodontic remediation.
2. Description of the Prior Art
In a series of studies published by G. A. Ilizarov beginning in 1988, techniques were described for lengthening endochondral bones and the surrounding soft tissue matrix. In particular, it was shown that the genesis of new bone tissue between facing surfaces of a newly cut bone is dependent upon tension-stress effects associated with the rate and frequency of distraction, namely the forced separation of said facing surfaces.
In a series of studies published since 1997 by W. H. Bell and others, it was shown that the osteogenesis principles elucidated by Ilizarov can be facilitated with intraoral appliances to achieve mandibular widening by symphyseal distraction. Such technique has been found useful in facilitating orthodontic remediation of mandibular crowding and other conditions. The appliance employed by Bell, now marketed as DynaForm.TM. by Stryker Leibinger Gmb H of Freiburg, Germany, is comprised of two frames interconnected by an advancing screw rotatively held by a fixed yoke mounted upon paired slide posts. Each frame is comprised of a rigid bar base and superior and inferior elongated arms orthogonally emergent from said base and terminating in distal extremities directed away from said bases. The base of one of said frames functions a yoke moveable upon said screw and slide posts. The arms are bendable to match the patient's buccal mandibular contour, and securement forks or rings are crimped onto the distal extremities. When proper fitting has been achieved, the extremities of the upper arms are secured to mandibular teeth, and the lower extremities are secured to mandibular bone.
Following installation of the Bell appliance bridging the site of osteotomy, carefully controlled distraction to distances of 7 to 12 mm. is accomplished by an activation tool in the nature of a specialized screwdriver employed by the dentist to engage the horizontally directed head of the screw, and rotate the screw.
An intraoral palatal expansion device available from Orthodesign of Chicago, Ill. has been described by Liou, et. al. in the Journal of Craniofacial Surgery, Vol. 9, No. 6, pgs 564-71, Nov. 1998. The Orthodesign distractor is comprised of two laterally opposed arms and an intervening rotatable screw device in the nature of a turnbuckle having oppositely threaded screws telescopically interactive with a barrel-like body having a faceted central region. When emplaced, the arms attach to the bone of the mandible, and the screw device extends transmucosally within the vestibule of the mandible. Although the method of operation of the screw device is not disclosed by Liou, the distraction is presumably achieved by rotation of the barrel-like body of the turnbuckle, employing an open-ended hex wrench that engages the faceted central region.
It has been found, however, that bone-borne distraction appliances such as Liou's having only two attachment sites produce a V-shaped bone regenerate which is not as stable or desirable as a parallel regenerate, particularly in the case of symphyseal mandibular widening. It is further necessary that means be provided whereby the telescopic screw is caused to be parallel with the desired vector of distraction.
In order to achieve best osteogenesis results, a carefully prescribed rate of distraction is required, such as two 0.5 mm. increments/day. Such regimen is best achieved when the patient, parent or other caregiver can administer the prescribed rated of distraction at home.
It is accordingly an object of the present invention to provide an intraoral screw-activated appliance for mandibular widening by symphyseal distraction osteogenesis.
It is a further object of this invention to provide an appliance as in the foregoing object which will produce a substantially parallel bone regenerate.
It is another object of the present invention to provide an appliance of the aforesaid nature which can be patient-manipulated to achieve a carefully prescribed rate of distraction.
It is a still further object of this invention to provide an appliance of the aforesaid nature which allows for precise surgical placement such that the axis of screw rotation is parallel with the desired vector of distraction.
It is yet another object of the present invention to provide an appliance of the aforesaid nature having a low profile which results in greater comfort to the patient.
It is an additional object of this invention to provide an appliance of the aforesaid nature which is durable, reliable, and amenable to low cost manufacture.
It is a further object of the present invention to provide a method for mandibular widening employing the appliance of the aforesaid nature.
These objects and other objects and advantages of the invention will be apparent from the following description.